30% is because most transactions, early on, were around $1. And processing fees are usually $0.25 + ~3% = so 28% of the average transaction. When you start app

30% is because most transactions, early on, were around $1. And processing fees are usually $0.25 + ~3% = so 28% of the average transaction. When you start applying that 30% to $15 spotify subs, $50 uber rides, $60 video game, then a bunch of in-app purchases ranging in value; the math falls apart and if you have scale to do it, the negotiated rate makes more sense for those businesses given the average transaction amount.